In a typical cellular radio system, wireless terminals, also known as mobile stations and/or user equipment units (UEs), communicate via a radio access network (RAN) to one or more core networks. The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” (UMTS) or “eNodeB” (LTE). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcasted in the cell. Another identity identifying the cell is also broadcasted in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations.
In some versions of the radio access network, several base stations are typically connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity.
Mobile telecommunications systems are normally statically configured with a parameter set defining the behavior of the system. The systems are based on standards which define radio bearers to carry traffic with different characteristics, e.g. speech, streaming video, or packet data. Standards such as the 3GPP standards referenced above also define different UE/RRC states. See, for example, 3GPP TS 25.331 V10.4.0 (2011-06), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Resource Control (RRC); Protocol specification (Release 10), incorporated herein by reference, which describes states such as CELL_DCH state, CELL_FACH state, CELL_PCH state, URA_PCH state, and the Idle state URA_PCH state. These names of these states are understood in view of the following channels/areas: Dedicated Channel (DCH); Forward Access Channel (FACH); Random Access Channel (RACH); UTRAN registration area (URA_PCH).
For each wireless terminal in the connected mode, a node of the radio access network, such as a radio network controller (RNC) node, determines in which of these states the wireless terminal operates. Whichever of the UE/RRC states a wireless terminal currently is in has consequences which affect, e.g., the UE battery consumption and the resource consumption in the mobile network.
For UTRAN (WCDMA) in particular the 3GPP standard defines the Radio Access Bearer (RAB) to carry the services, where the Interactive RAB is specified for best effort traffic. The 3GPP standard also defines UE/RRC states such as CELL_DCH, CELL_FACH, CELL_PCH, and URA_PCH, mentioned above.
Packet data services have escalated, particularly with the introduction of wireless terminals in the form of devices such as Smartphones, and with personal computers (PCs) now widely participating in the mobile networks. Most of the packet traffic is based on the internet protocol (IP), e.g., internet services, and is normally treated as best effort traffic in the mobile network. Internet services are of many types and different characteristics, e.g. web browsing, chat, email, file sharing, and video streaming
Within an Internet Protocol (IP) flow there are typically times of activity and times of inactivity. Periods of activity will be separated by times of inactivity of different length. Within the IP flow, a burst may for example be defined by IP packets arriving with a maximum inter-arrival time (IATmax). The Idle Time Between bursts (ITB) is defined as the time between the last packet in one burst and the first packet of the next. A burst, inter-arrival time (IAT), and Idle Time Between bursts (ITB) are illustrated in FIG. 2.
As mentioned above, a radio access network node such as the radio network controller keeps track of the UE/RRC state in which a wireless terminal is currently operating and also governs the transition of the wireless terminal between UE/RRC states. In other words, the radio network controller determines when a wireless terminal should transition from one UE/RRC state to another state. Parameters to govern the transition between UE/RRC states are normally timer based. FIG. 3 generally depicts that, when switching to a higher state, a wireless terminal may be required to transition from one UE/RRC state to another UE/RRC state upon expiration of a timer. The timer may be activated or initiated by some UE-related network activity, e.g. forwarding of an IP packet to/from the UE. The timer may expire due to some UE-related inactivity, e.g., no IP packet forwarded to/from the UE. Expiration of the timer may prompt the transition from one UE/RRC state to another UE/RRC state. Transfer to a state of higher activity is normally transmission-triggered, e.g., filling of a buffer.
High Speed Packet Access (HSPA) generally employs two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), and as such extends and improves the performance of existing WCDMA protocols. With HSPA it is now possible to provide mobile broadband since the peak bit rates reach up to 42 Mbps (3GPP R8) in downlink, and 11 Mbps (3GPP R8) in uplink. For 3GPP R9 the peak rates are doubled. Thus, HSPA may be seen as a complement and replacement to other broad band access such as Asymmetric Digital Subscriber Line (ADSL).
As mentioned above and illustrated in FIG. 1, the Idle, Cell_DCH, Cell_FACH, URA_PCH, and Cell_PCH are the five RRC protocol states. Data transfer between the terminal and the network is only possible in Cell_FACH and Cell_DCH states. The Cell_DCH state is characterized by dedicated channels in both the uplink and the downlink. This corresponds to continuous transmission and reception and has the highest battery consumption. The Cell_FACH state does not use dedicated channels and thus allows lower battery consumption, at the expense of a lower uplink and downlink throughput. Thus, in addition to showing the RRC states, FIG. 1 also shows serves as an example state transition diagram. As understood from FIG. 1, the system typically does state transition due to amount of data in the RLC send buffers and due to the length of transmission inactivity.
In the example state transition diagram of FIG. 1, down-switch from CELL_DCH is based on inactivity timers. These may be set differently depending on traffic types, based on RNC load, with respect to UE power consumption or even specifically per user. A different approach is to use adaptive channel switching by predicting the time until the next data activity, i.e. to predict the inter-arrival time (IAT) between data bursts. Examples of adaptive channel switching are described, e.g., in U.S. provisional patent application 61/544205, filed Oct. 6, 2011, entitled “DYNAMIC ”RADIO RESOURCE CONTROL STATE SWITCHING, and incorporated herein by reference in its entirety.
There is a difference in processor load for the RNC associated with staying in the different states and to switch between the states. The load of residing in CELL_DCH may be approximately 40 times that of staying in one of the lower states, e.g. CELL_FACH or URA_PCH. Hence from the RNC perspective, it is most efficient to avoid CELL_DCH except when needed due to requirements on data transmission rate. However, since there is also a processor load associated with switching, down-switching is not economical unless the UE may stay in the lower state for a certain time (depending on the specific RNC load implication).
The current or state-of-the-art solution is to base the decision of when to down-switch to a lower state on idle time which is executed when the associated down-switch timer expires, as illustrated by way of example in FIG. 3. This solution has several drawbacks which are, e.g., associated with the random nature of IAT or when the next data activity will occur. One such drawback is the probability that there is a long time until next data activity when the down-switch timer expires may be varying between applications, users etc. This implies that using down-switch timers is an inexact method to determine an optimal down-switch time. Another drawback is that adaptive channel switching techniques which use a prediction of the time to next data activity are also inexact in the sense that predictions are not always correct. That is, there is always a probability that an erroneous prediction is made.
In the above regard, of special importance is the case when the switching decision is to down-switch, either because of an expired timer or a long predicted IAT. If this decision is erroneous, the result is a considerable and unnecessary load caused by a down-switch and the following immediate up-switch. Avoiding this error is important in order to minimize the RNC load. A second type of error is when the down-switch is delayed, either by a too long down-switch timer or erroneous prediction.
Hence, due to the random nature of the IATs or time to next data activity, it is impossible to reach the theoretical optimal performance, i.e., the minimum possible RNC load given a trace of IATs. This cannot be avoided since the IAT are not known when the switching decision is taken. However, optimizing the prediction and decision taking is of considerable importance to minimize RNC load at a given traffic load.